This invention relates generally to a fluid conduit, and more particularly to a flexible fluid conduit for transporting a pressurized fluid between a fluid source and an actuator mounted on, for example, an articulated portion of a machine such as a rotor blade on a rotary wing aircraft.
Fundamental to the operation of many machines, devices, or instrumentalities is the ability to control an articulated part which moves relative to the rest of the instrumentality, device or machine. For example, many turbine or fan devices have facility for dynamically controlling the pitch of their rotor blades. Pitch is a factor in determining the dynamic forces acting on the blade and, hence, determining the forces applied by the blades to the frame of the instrumentality.
Control of blade pitch generally originates in the frame of the instrumentality which is stationary relative to the articulated portion of the instrumentality. Control of the variable pitch of the blades of, for example, a wind turbine, a ship or airplane propeller, and the main rotor or the tail rotor of a helicopter are all originated within a rotating hub of the wind turbine, ship, airplane or helicopter, respectively.
In a rotary wing aircraft application, such as a helicopter, an active rotor control system can be used to reduce vibratory loads and externally radiated noise originating from the main rotor system. Actively controlled blade actuation systems control the pitch of the rotor blades or the pitch of leading or trailing edge flaps on the blades during flight. An actuator mounted on the blades is used to control the movement of the blades or flaps. While actuation requirements are dependent on the specific application and the capabilities of the control software and hardware, the actuation system must be designed to produce sufficient force to counter both aerodynamic and inertial loads while being small in size and light in weight. Further, the actuation system must be capable of providing a sufficient amount of force to overcome the air loads acting on the flap during normal flight (i.e., when the flap is being held motionless relative to the blade). In order to meet these design requirements, a hydraulic actuation system which supplies pressurized fluid to the actuators is preferred for several reasons. For example, fluid compressibility is low which provides better control over flap motion, and hydraulic actuators provide the greatest work output on a per unit volume and a per unit weight basis.
Generally, hydraulic actuation systems include a source of fluid which is remotely located from the associated actuator. The remote location of the source of fluid is what allows the actuators to be both small and light weight.
The fluid path from the actuator fluid source to the helicopter blade or flap actuator bridges a multi-degree of freedom joint which provides for rotor blade articulation in pitch, flapping, and lead/lag. The joint must be unrestrained in its movement by any fluid line linking the fluid source and actuator which bridges the joint. Additionally, the linkage which bridges the joint must not significantly add to the force required to move the rotor blade in the joint.
Ordinarily a simple flexible hose would be used to accommodate motion of the multi-degree of freedom joint. However, because the wall stiffness of the flexible hose is low (allowing the hose to be flexible to motion), the flexible hose expands in diameter with increased fluid pressure. In high performance hydraulic actuator systems, the elastic expansion and contraction of a flexible hose carrying fluid to or from the actuator consumes power which would otherwise be transmitted to the actuator. Given that there is a desire to keep the fluid source as small as possible, this power loss is undesirable. Moreover, the lapse time between a control signal commanding the fluid source to supply or remove fluid from the actuator and the actuator actually moving can be long. Thus, a flexible fluid hose can reduce the responsiveness of a hydraulic actuator system which results in reduced performance. An active hydraulic actuator system in as demanding an environment as a rotary wing aircraft cannot accommodate the compliance of a flexible hose of the length needed to bridge the flexible joint.
Metal piping, due to its rigidity, would allow an actuator system utilizing pressurized fluid to meet performance requirements. Metal pipe is robust, inexpensive, and easily changes direction via elbows or, if thin wall metal pipe is used, by bending. The diameter of metal pipe changes little with an increase in fluid pressure since the metal is a stiff-walled conduit. Unfortunately, rigid metal fluid lines are intended for stationary connections and cannot accommodate relative motion between a fluid source and an actuator associated with the articulated portion of machinery.
For the foregoing reasons, there is a need for a flexible fluid conduit for transporting a pressurized working fluid between a fluid source and an actuator. The fluid conduit should be suitable for a high performance hydraulic actuation system on articulated machines, devices, or instrumentalities, wherein the actuator is mounted on the articulated portion of the machine. The conduit should be compliant enough to bridge a multi-degree of freedom joint between the actuator fluid source and the actuator without restraining or adding to the force required to move the joint. The conduit should also have high wall stiffness to minimize power loss and lapse time in carrying fluid to or from the actuator.